In the oil and gas industries, disconnect devices are typically used to separate a bottom hole assembly (BHA) from a drill string if, for example, the BHA becomes stuck. Once the drill string has been disconnected from the BHA, the operators can then attempt to recover the stuck BHA with a “fishing” tool. However, in situations where recovery of the BHA is impractical or impossible, the stuck BHA will be abandoned and drilling will recommence along a different route with a new BHA attached to the drill string.
Typical methods for disconnecting a drill string from a stuck BHA involve dropping a dart, ball or mud slug of high density fluid from the surface to interact with a shear pin or other locking device and actuate the separation. For example, WO-A-03/029605 (Weatherford/Lamb, Inc.) describes a disconnect device having two portions connected by a lock nut. The two portions separate when a predetermined fluid force is applied to a piston in the disconnect device causing a tensile sleeve to fail. In one particular embodiment, the tensile sleeve's failure permits an annular piston to dislodge a wedge sleeve from the lock nut, thereby permitting separation. Such arrangements require the circulation of drilling mud to transport the interacting article (dart, ball or mud slug). However, this is often impossible when the BHA becomes stuck. Another disconnect device that relies on the circulation of fluid is described in GB-B-2351101. The GB-B-2351101 device comprises a radially expandable locking ring that is configured to expand and thereby disconnect the device.
Alternatively, drill strings can be separated without using specialist tools by performing a precise series of “back off” movements and rotations such as turning the drill string leftward and overpulling to affect a release. This technique is often complicated and difficult and is consequently unreliable.
A third option is to separate the drill string above the point at which it is stuck by explosive means. US-A-2004/0200343 (Titan Specialties, Ltd.) describes a pipe severing tool that is positioned into a well bore before exploding to actuate separation. The tool comprises explosive pellets and electrically initiated exploding wire detonators (EBW) that are positioned at opposite ends of a tubular housing for simultaneous detonation by a capacitive firing device.
This technique is often used as a last resort and usually requires the skills of a specialist team which may take several days to arrive at the rig and sever the drill string. Due to the high operating costs of drill rigs, this significant time period of non-operation can lead to substantial financial losses which are highly undesirable. Additionally, the damaged end of the drill string must be replaced before a new BHA can be connected and drilling can recommence. Furthermore, most explosive disconnection techniques are dependent upon gravity for locating the explosives close to the point at which the tool is stuck. It follows that explosive disconnection is generally not an option for the disconnection of a BHA in a horizontal section of the well bore.
There is therefore a need to provide a disconnect device that allows for a controlled disconnect from the BHA with no physical input from the surface other than mechanical signals. The present invention satisfies this need and allows for the drill string to be retracted undamaged so that drilling can recommence as quickly and as easy as possible following the disconnection. It is a further object of the present invention to provide a secure disconnect device that will only actuate when the tool is stuck and the operator wishes to do so.
It is a further object to provide a tool that is actuated by controlled movements of the tool without other signalling from the surface so that tools such as circulating subs can be reliably activated when required.
WO-A-2010/061231 discloses a selectively operable downhole tool for incorporation in a drill pipe for selective operation of the downhole tool from surface level when the tool is in a wellbore, said selectively operable tool comprising:
a controller electrically powered by a power source separate from surface level;
a first sensor of the controller to detect a dynamic variable of the tool in the wellbore and produce an output signal dependent thereon;
a second sensor of the controller to detect a mechanical signal transmitted from an operator at surface level;
a first motor driven by the power source under the control of the controller when said mechanical signal is received; and
a first actuator driven by the first motor to actuate the tool; wherein
the controller switches between at least two states in response to changes in said dynamic variable, only in said second state the controller being receptive to said mechanical signal from the operator to drive the first motor.
Of course, the dynamic variable is frequently controlled to a greater or lesser extent by the operator. Variables such as vibration, temperature, hydrostatic pressure, are consequences of the situation but are not specifically determined by the operator and thus are essentially independent. However, other variables are more clearly under the control of the operator such as rotational accelerations or compressive forces or pump pressures, for instance. Mechanical signals transmitted by the operator from the surface typically take the form of changes in pump pressure, rotation of the drill string or load imposed on the drill string. Therefore, said first and second sensors may conceivably be detecting the same variable, except that, in the case of the first sensor, the detection is in response to some operational condition that serves to switch the controller between said states and in the case of the second sensor, the detection is in response to a specific operator signal that serves to cause the controller to actuate the tool. Even then, in some instances, the operational condition that causes switching between states of the controller might be deliberately induced to cause the controller to switch states.
WO-A-2010/061231 also discloses a disconnect tool for incorporation in a drill string between a downhole assembly and a drill pipe to selectively disconnect the downhole assembly from the drilling pipe when the downhole assembly is stuck in a wellbore, said disconnect tool comprises:
first and second parts that are releasably connected to one another by a disengagement apparatus, one of said first and second parts being adapted for connection to said drilling pipe and the other of said first and second parts being adapted for connection to said downhole tool, wherein
said disengagement apparatus comprises an actuator and first and second coupling elements,
the first coupling element comprising:
a die retention sleeve, axially movable in the first part from an operational position towards a disconnect position of the disengagement apparatus;
a clutch housing, disposed within said die retention sleeve, said clutch housing being axially and rotationally fixed in the first part;
windows in said clutch housing circumferentially spaced around the clutch housing; and
radially displaceable capture dies housed in said windows, and
the second coupling element comprising:
an interface of said second part adapted to be engaged by said capture dies, wherein,
the actuator moves the retention sleeve between its operational and disconnect positions, so that
when the first and second parts are engaged with one another and the retention sleeve is in its operational position, the capture dies bear against both the die retention sleeve and said interface of the second part to lock said first and second coupling elements and parts together, and
when the retention sleeve is moved to its disconnect position, the capture dies can move radially to disengage from said interface so that said coupling is unlocked and said parts can separate.